Video signal processing circuitry of the type used for processing, for example, composite video signal, typically include a burst locked clock signal generator for generating a reference or clock signal to aid in demodulation of the chrominance component of the composite signal, or in the case of digital signal processing apparatus, to provide a sampling and processing clock signal. The burst locked clock generator nominally is coupled to be responsive to the burst component of the composite signal, prior to the separation of the luminance and chrominance components. However it has been found to be advantageous, particularly in digital processing systems, to couple the burst locked clock generator at a point subsequent luminance and chrominance separation. In so doing the burst locked clock generator can be made responsive to a burst component which has been processed by automatic chrominance correction, ACC, and thereby provide a more accurately phased clock signal, particularly for received signals of low amplitude.
Currently the circuitry of choice for separating the luminance and chrominance components includes a comb filter. Separating the luminance and chrominance components via comb filtering involves summing signals from at least two horizontal lines of video signal. As a result the separated burst component is the sum or average of the burst signal from at least two lines. This averaging process tends to remove phase errors from the resultant burst component. This is particularly problematic in systems using adaptive comb filters wherein contributions to the resultant signal are derived from different lines at different times. Alternatively the comb filtering process may be viewed as low pass filtering the burst signal, and thereby slowing the response time of the burst locked clock generator.